Introduce config.dom_testing_default_html_version and use Rails::Dom::Testing to parse HTML in test helpers

[flavorjones]

Motivation / Background

Some early users of Rails edge reported test breakage due to the change in #48523 that updated test helpers to use Nokogiri's HTML5 parser.

After discussing with Rafael, he suggested that we introduce a Rails config parameter so users may opt into this change at their convenience, essentially wrapping a config param around the changes in #48523.

This PR takes that idea a step further and groups all the test helpers from ActionView::TestCase, ActionDispatch::Assertions, and everything in Rails::Dom::Testing under a single config param:

config.dom_testing_default_html_version

As a result, by setting this config to either :html4 or :html5, a developer can control the HTML parser used by all the test helpers in Action View, Action Dispatch, and Rails::Dom::Testing; and some assertions support overriding that default for individual tests.

Detail

• new config parameter config.dom_testing_default_html_version, which is injected into Dom::Rails::Testing via the railstie in Allow user to choose the HTML parser used rails-dom-testing#109
  • the value of that param is :html5 in Rails 7.1, and :html4 in earlier config versions
  • though, on JRuby, where Nokogiri::HTML5 is not supported, this will always be :html4
• Action View and Dispatch test helpers use Rails::Dom::Testing.html_document or .html_document_fragment to ensure the desired HTML parser is used
  • Update dependency on rails-dom-testing to ~> 2.2

Additional information

Note that integration testing across gems like this is challenging, but I have actually fired up a Rails app using this PR and rails/rails-dom-testing#109 together, and it worked as expected.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[flavorjones]

I can't reproduce the failures in buildkite (cd railties; bin/test test/generators/app_generator_test.rb), not sure what's going on there.

[guilleiguaran]

I've seen similar errors in the past when trying to point a gem to a git repo in the Gemfile, for some reason the gem can't be found when the app generators tests execute bundler

[flavorjones]

@rafael I've updated this to use rails-dom-testing ~> 2.2, I think it's ready for full review.